1. Field of the Invention
This invention relates to a semiconductor integrated circuit such as a standard cell, and a method of design thereof.
2. Description of Related Art
Automated design techniques for automatically determining the placement and routing of semiconductor integrated circuits have recently improved so much, this automatic design is widely used in the semi-customized IC such as standard cells. However, if several circuits such as macro cells are formed on the same semiconductor substrate, it often happens that the power system of the power wiring for one circuit is required to be separated from that of another circuit. For example, if the operating voltage of one circuit differs from that of another circuit, the power wiring that supplies power to one circuit is required to be separated from the power wiring that supplies power to the other circuit. The shape of the power wiring becomes complicated, to ensure that the power wires do not cross. Such power wires cannot be laid out by automated routing alone. Thus the designers have to do all or part of the work of laying out the power wiring manually. The result is an increase in the time required for power wiring layout.
An objective of this invention is to provide a semiconductor integrated circuit and a method of design thereof that makes it possible to reduce, or even eliminate, the manual work that must be done by the designers in addition to the automated routing of power wiring.
(1) This invention relates to a method of designing a semiconductor integrated circuit which comprises a circuit block, a first power wire for supplying power to circuitry within the circuit block, and a second power wire of a power system that differs from a power system of the first power wire,
wherein the first power wire and a third power wire are provided within the circuit block; and
wherein the third power wire has a bent portion, is separated from the first power wire, and has the same power system as the second power wire; and
wherein the method of designing a semiconductor integrated circuit comprises:
a first step of determining the position of the circuit block; and
a second step of automatically placing the second power wire in such a manner that the second power wire is connected to the third power wire after the first step.
Examples of power systems with different power wires are given below. If the operating voltage of one circuit differs from that of another circuit, the power wire of one circuit will have a power system that differs from that of the power wire of the other circuit. Similarly, if one circuit is a digital circuit and another circuit is an analog circuit, the power wire of one circuit will have a power system that differs from that of the power wire of the other circuit, even if they use the same voltage.
This aspect of the invention makes it possible to have a power system for one wire that comprises the second power wire and the third power wire. This aspect of the invention also makes it possible to reduce, or even eliminate, the work of laying out the power wiring manually, even if that one power wire has a complicated shape such as a polygonal shape with five or more sides. In other words, since the third power wire has a bent portion such as a corner portion, this third power wire can be used to form a portion that has a complicated shape for that one power wire, making it possible to layout the second power wire automatically.
This invention also relates to a semiconductor integrated circuit comprising a circuit block, a first power wire for supplying power to circuitry within the circuit block, and a second power wire of a power system that differs from a power system of the first power wire, formed on the same semiconductor substrate,
wherein the first power wire and a third power wire are provided within the circuit block; and
wherein the third power wire has a bent portion, is separated from the first power wire, and has the same power system as the second power wire. The method of designing a semiconductor integrated circuit in accordance with this aspect of the invention, can be used in the design of such a semiconductor integrated circuit.
(2) In the semiconductor integrated circuit and method of design thereof in accordance with this invention, the third power wire may be placed on an outer side of the first power wire.
(3) In the semiconductor integrated circuit and method of design thereof in accordance with this invention, the third power wire may comprise: a first edge that extends in a first direction and is connected to the second power wire that extends in a second direction; and a second edge that extends in the second direction and is connected to the first edge.
xe2x80x9cFirst directionxe2x80x9d means a first priority routing direction during the automated wiring, by way of example. xe2x80x9cSecond directionxe2x80x9d means a second priority routing direction during the automated routing, by way of example.
(4) In the semiconductor integrated circuit and method of design thereof in accordance with this invention, the circuit block may be integrated with an I/O port for the circuit block. This makes it possible to reduce the work of connecting the circuitry of the circuit block to the I/O port for that circuit block, during the automated routing stage.
(5) In the semiconductor integrated circuit and method of design thereof in accordance with this invention that was described in (4), the first edge and the second edge may be provided between the I/O port and another I/O port. This simplifies the separation of power systems for the power wires for the I/O port and the other I/O port.
(6) In the semiconductor integrated circuit and method of design thereof in accordance with this invention, the third power wire may comprise:
a first edge that extends in a first direction and is connected to the second power wire that extends in a second direction;
a second edge that extends in the second direction and is connected to the first edge;
a third edge that extends in the first direction and is connected to the second edge; and
a fourth edge that extends in the second direction and is connected to the first and third edges;
such that the first power wire is surrounded by the first to fourth edges.
The first to fourth edges are formed to surround the first power wire. Therefore, any of the first to fourth edges can be freely selected in accordance with the position of the circuit block, for connection to the second power wire. It is therefore possible to place the circuit block at any position within the semiconductor integrated circuit region.
(7) In the semiconductor integrated circuit and method of design thereof in accordance with this invention, the first power wire may comprise an encircling power wire. An encircling power wire is a power wire such that one end portion is connected to the other end portion thereof. The shape of the encircling power wire could have a circular form or a rectangular form, by way of example.
(8) In the semiconductor integrated circuit and method of design thereof in accordance with this invention, the second power wire and the third power wire may form another encircling power wire.
(9) In the semiconductor integrated circuit and method of design thereof in accordance with this invention, a potential supplied by the first power wire may differ from a potential supplied by a power wire that comprises the second power wire and the third power wire.
(10) In the semiconductor integrated circuit and method of design thereof in accordance with this invention, a potential supplied by the first power wire may be the same as a potential supplied by a power wire that comprises the second power wire and the third power wire.
(11) In the semiconductor integrated circuit and method of design thereof in accordance with this invention, the circuit block may comprise a macro cell.
(12) In the semiconductor integrated circuit and method of design thereof in accordance with this invention, the circuit block may comprise at least one of ROM, RAM, an analog circuit, a control circuit, and an interface circuit.
(13) The semiconductor integrated circuit and method of design thereof in accordance with this invention may further comprise a step of determining a position of another circuit block supplied with power by a power wire that comprises the second power wire and the third power wire, between the first step and the second step.
(14) In the semiconductor integrated circuit and method of design thereof in accordance with this invention, the other circuit block may comprise a macro cell.
(15) In the semiconductor integrated circuit and method of design thereof in accordance with this invention, the other circuit block may comprise a random logic circuit.
(16) In a method of designing a semiconductor integrated circuit in accordance with this invention, information on the circuit block, information on the other circuit block, information on the first power wire, information on the second power wire, and information on the third power wire may be stored in a library.
(17) In a method of designing a semiconductor integrated circuit in accordance with this invention, positions of the circuit block and the other circuit block may be determined by automatic placement.
(18) In the semiconductor integrated circuit and method of design thereof in accordance with this invention, the semiconductor integrated circuit may comprise at least one of a standard cell, a gate array, and an embedded array.